The present invention relates to a cylinder lock provided with an effraction-resistant device.
A cylinder lock conventionally comprises a body which has a cylindrical seat that rotatably accommodates a plug. A bit is rotationally rigidly coupled to one end of the plug for the actuation of a bolt or latch. A keyway is formed axially in the plug and intersects a first plurality of holes which are formed on a radial plane of the plug and in which a first plurality of pins is guided. The pins have conical ends which protrude into the keyway and on which the key is meant to act with a coded longitudinal portion thereof. A second plurality of holes, equal in number to the first plurality, is formed in the body so that each hole, in a specific angular position of the plug, is aligned with a respective pin. A plurality of complementary pins is guided in the second plurality of holes together with a plurality of springs which, in said specific angular position, keep each complementary pin in contact with a respective pin by acting on the plurality of complementary pins.
When the key is extracted from the keyway, the springs push the complementary pins and the pins into a position in which the complementary pins intersect the plane on which the seat and the plug mutually couple, preventing the rotation of the plug.
Viceversa, when the key is inserted, the plane of contact between the pins and the complementary pins is shifted until it lies on the coupling plane, allowing the plug to rotate.
The weak point of cylinder locks consists in that the pins can be accessed from outside through the front opening of the keyway and, by using adapted picking tools, can be moved fraudulently so as to allow the plug to turn.
In order to obviate fraudulent opening of cylinder locks with the above method, it has already been thought to arrange auxiliary tumblers which are accommodated in holes of the plug and which, when the appropriate key is used, remain inside the plug and do not prevent its rotation. Viceversa, if the key is forged, the auxiliary tumblers are pushed outward until they engage in notches of the plug seat so as to prevent its rotation. The effectiveness of the tumblers is due to the fact that if they are viewed from outside they cannot be distinguished from ordinary pins and therefore they can mislead the burglar. However, once these pins have been identified, they can be bypassed by providing appropriate longitudinal cutouts on the forged key (in this case one speaks of a xe2x80x9cslotted keyxe2x80x9d).
The aim of the present invention is to provide a lock in which the auxiliary tumblers and the key are structured so that the effectiveness of the auxiliary tumblers is not compromised by a forged slotted key.
Within the scope of this aim, an object of the present invention is to provide a lock in which the auxiliary tumblers are structured so as to neutralize attempts to open the lock when the key is not inserted.
This aim, this object and others which will become apparent hereinafter are achieved with a cylinder lock which comprises a body, a cylindrical seat formed in said body, a plug which can rotate in said seat, an actuation bit which is rotationally rigidly coupled to said plug, a keyway which is formed axially in said plug, characterized in that it comprises at least one hole which is formed in said plug and intersects said keyway, said hole being provided with two shoulders, of which one lies further outward and the other one lies further inward with respect to the surface of the plug, at least one auxiliary tumbler accommodated in said hole and comprising an auxiliary pin, an auxiliary complementary pin and a spring which acts by expansion between said auxiliary pin and complementary pin and is such as to allow said tumbler to assume an elongated configuration, wherein said pin and said complementary pin are mutually spaced and can be axially offset angularly with respect to each other, or a shortened configuration, in which said pin and said complementary pin are aligned in mutual abutment and cannot be axially offset, said tumbler, when the key is removed or when a forged key provided with a removed portion is inserted, being adapted to assume said elongated configuration by virtue of which said auxiliary pin is kept rested against said inner shoulder and said auxiliary complementary pin is kept at such a level as to allow angular strokes with respect to said auxiliary pin and the engagement of said complementary pin on said outer shoulder, while the end of said complementary pin remains engaged in a notch of said cylindrical seat, and further characterized in that said key is provided with an elastic element adapted to cooperate with said auxiliary tumbler in order to allow, when the key is inserted, the compression of said auxiliary tumbler in the shortened configuration and the disengagement of said tumbler from said notch and the consequent rotation of said plug.